A rechargeable battery, as its name implies, is capable of repeatedly being charged, storing the charge and delivering the charge to the tool or other device to which the battery is attached. Rechargeable batteries have, over the years, evolved into reliable power sources for powered surgical tools used in operating rooms to perform surgical procedures. The use of a battery eliminates the need to provide a power cord connected to an external power source. The elimination of the power cord offers benefits over corded surgical tools. Surgical personnel using this type of tool do not have to concern themselves with either sterilizing a cord so that it can be brought into the sterile surgical field surrounding the patient or ensuring that, during surgery, an unsterilized cord is not inadvertently introduced into the surgical field. Moreover, the elimination of the cord results in the like elimination of the physical clutter and field-of-view blockage the cord otherwise brings to a surgical procedure.
A rechargeable battery typically includes a housing. One or more rechargeable cells are disposed in the housing. The cells are formed from material capable of storing electrical charge. Presently cells are made from nickel or lithium based materials. Typically, plural cells are disposed in the housing. The cells are connected together in series and/or parallel. Mounted to the housing are at least two contacts. One contact, the cathode, is the contact through which current flows out of the battery. The second contact is the anode, essentially the ground terminal for the battery. The cathode and anode are the terminals to which a charge is applied to the cells. The cathode and anode terminals are also the terminals connected to the complementary terminals of the tool the battery is employed to energize. The current flows out of the cathode terminal to the complementary component in the terminal that requires a current to operate.
Some batteries are also provided with supplemental components. These components include internal sensors, data collection circuits, memories or control processors. These components: monitor the environment to which the battery is exposed; store data regarding the use of the battery; or store data regarding the tool to which the battery is attached. The Applicant's Assignee's U.S. Pat. No. 6,018,227, BATTERY CHARGER ESPECIALLY USEFUL WITH STERILIZABLE RECHARGEABLE BATTERY PACKS, issued 25 Jan. 2000 and is US Patent Pub. No. 2007/0090788/PCT Pub. No. WO 2007/050439 A2, SYSTEM AND METHOD FOR RECHARGING A BATTERY EXPOSED TO A HARSH ENVIRONMENT, published 26 Apr. 2007, the contents of both which are explicitly incorporated herein by reference, disclose batteries that include these supplemental components. When a battery is provided with one of these supplemental components, the battery housing includes a supplemental contact. This supplemental contact is the contact through which signals are received from and/or transmitted to the supplemental components.
Batteries used to power surgical tools are exposed to adverse environmental elements to which batteries used for non-medical uses are seldom exposed. For example, during a surgical procedure, a medical battery may be exposed to blood or other body fluid. Tissue removed from the patient may adhere to the battery. While not an intended part of any procedure, a battery may be exposed to a saline solution. To eliminate the risk of patient's being infected during the course of the medical procedure, it is therefore standard practice to, between surgical procedures, sterilize the battery. This cleaning/sterilization process typically involves rinsing the battery to remove contaminates that are readily visible on the surface of the battery.
During any one of the above events, a liquid bridge can form between the cathode and anode contacts. These liquids, even if just tap water, can form a conductive bridge between the cathode and the anode. If the bridge is conductive, there is current flow between the contacts. The conductive liquid undergoes an electrolytic reaction with the metal forming the anode contact. As a consequence of this reaction, a layer of metal oxide forms on the anode terminal. This oxide layer functions as an impedance layer. The presence of this impedance layer reduces the efficiency of the both the charging of the battery and of the battery to deliver charge to the tool to which the battery is attached.
If the battery is provided with supplemental components, the exposure of its terminals to liquid may also cause oxidation of the data terminal. The resultant oxide layer, if of sufficient size, may essentially function as a resistor in series with the data terminal. The presence of this oxide layer can attenuate the levels of the signals applied to or read out from the battery over the data terminal. This voltage attenuation may be such that they cannot be processed by the components to which they are applied.
Further, it is now a common practice to design a battery so it is a part of specific cordless tool system. The battery and the tools the battery is intended to charge are designed to cooperate in a specific manner. For example, in the event a processor internal to the battery determines that the battery is in a specific state, the battery may communicate this information to the attached tool. A processor internal to the tool, in response to this information, then regulates the operation of the tool based on the battery state information. For example, if a battery processor determines that the associated cells may be in a low charge state, the processor may communicate this information to a processor in the attached tool. In response to this information, the tool processor may attenuate the operation of the tool power generating unit to prevent the sudden complete discharge of the battery.
A manufacturer of this type of tool system may be reluctant to allow a battery to be used with tools that the manufacturer is not sure will work appropriately when attached to the battery. To avoid this unintended use of the battery, it is a practice to design the battery so that the battery processor controls whether or not the cells source current to the attached tool. It has been suggested to design a battery so that when a tool is first attached to the battery, the battery processor allows current flow to the attached device for a relatively short amount of time. This would allow the processor internal to the tool to power up and then exchange recognition codes with the battery processor. If the battery processor does not receive the appropriate recognition codes within a defined time frame, the battery processor, blocks the sourcing of electrical current to the tool.
The above system would prevent a battery from serving as an extended power source for a tool or other device for which the battery is not specifically designed. However, during the period in which the processors internal to the battery and tool are exchanging signals, current can be sourced to the power generating unit internal to the tool. When initially attached to battery, a tool not intended for use with the battery could function. Only after the battery processor determines that it has not received the appropriate recognition codes, does the battery processor terminate the sourcing of current tool. Thus, for at least a few seconds, the tool will run and then shut off. This could provide the individual using the tool the mistaken impression that, since the tool started and stopped, there is a malfunction with either the tool or the battery.
Moreover, an individual, for either mischievous or malicious reasons, with knowledge of the features of this type of battery, could tamper with the battery so as to cause drainage of an appreciable fraction of the cell's stored charge.